The invention relates to a method for traction control (ASR) which will aid initiating movement on an incline.
The simultaneous use of ABS (anti-skid braking system) components provided in automobile brake systems for traction control or as an aid in starting movement uphill or on a slippery surface is known from British Pat. No. 2,119,883. The patented device makes use of a special embodiment of an anti-skid system, the so-called ABS-2. This kind of known anti-skid system is provided with pressure fluid tanks combined with a recirculating pump. In the ABS step of pressure reduction, the pressure fluid reservoirs receive pressure fluid from the wheel brake cylinders through the ABS control valves, which are usually of the 3/3-way type, switched accordingly. Via the recirculating pump, which communicates with the reservoir tanks or chambers, the pressure fluid then reaches the connecting line between the master brake cylinder and the wheel cylinders; as related to the standpoint of the master brake cylinder, the connection is typically located upstream of the ABS control valves.
To achieve traction control on the basis of this known, separate ABS-2, British Pat. No. 2,119,883 provides an additional pressure tank, which in the event of a traction control function communicates via a 3/2-way valve with the pressure line leading to the wheel brake cylinders. Depending on the triggering of the ABS control valves for the ASR (traction control) function to be achieved, the fluid pressure available in this pressure tank reaches whichever wheel brake cylinder on the driven axle is to be selectively triggered to attain a locking differential effect; in that case, the ABS control valves are triggered inversely, which can be done via a suitably embodied control logic circuit for the combined ABS/ASR situation.
For economical yet fully high-quality traction control by using the components of the anti-skid control means, a further pressure controlled reversing valve, an overpressure valve and a pressure switch are provided in addition to the pressure tank and the magnet valve connecting it with the wheel cylinders.
The pump is designed as an aspirating pump, and whenever there is not enough pressure in the tank, upon the switchover of the magnet valve, for attaining traction control functions, the pump is triggered either via the pressure switch or directly by the electronic control unit, so that it feeds pressure fluid into the pressure tank or into the brake circuit connected to it. The additionally provided pressure controlled reversing valve opens when a predetermined minimum pressure is attained at the outlet of a feed pump storage chamber, and thus causes pressure fluid to flow from the master brake cylinder to the reservoir chamber and provides for refilling. Finally, the check valve that is also provided assures that the pressure between the magnet valve that switches over when ASR functions are to be performed and the ABS valves do not become excessively high in the vicinity of the wheel brakes.
U.S. Pat. No. 4,416,347 also discloses the use of ABS components for traction control or as an uphill movement starting aid, with corresponding "inverse" triggering of the ABS control valves and modification of other existing components, although if both driven wheels are spinning very markedly, additional means are provided, which lower the output power of the driving engine, by exerting influence on the mechanical connection between the gas pedal and the throttle valve in the intake tube of the engine. This can be done with the aid of an electromagnetically triggered 3/2-way valve.
In a further combined apparatus for achieving both anti-skid and traction control functions using the same components, the ABS system is assigned an additional pressure tank, which serves to supply braking pressure in the event of traction control functions. This pressure tank can be charged under valve control with the aid of the recirculating pump of the anti-skid system; the recirculating pump feeds into this tank during the pressure reduction phases of the traction control. Outside such control phases, or in other words during normal operation, the pressure tank can be recharged either by actuating the vehicle brake, or, if the vehicle is stopped or is in a non-braked operating state, by automatic activation of a charging circuit with the cooperation of the recirculating pump.
Here, precisely as in the combined systems discussed earlier above, additional hardware components are needed--that is, at least one additional pressure tank and hydraulic lines connecting it with the other components--and the required pressure for achieving traction control functions is always drawn from this additional pressure tank.